钢筋混凝土和钢纤维混凝土杂散电流腐蚀实验研究

依据地铁杂散电流对地下金属物质发生阳极氧化的电化学腐蚀机理,模拟了钢筋混凝土和钢纤维混凝土试件的杂散电流腐蚀实验。通过两种不同材料在相同的杂散电流环境中进行模拟腐蚀比较,分析了钢筋混凝土和钢纤维混凝土在抵制杂散电流腐蚀的耐久性和破坏形式方面的异同。结果表明,两种材料的耐久性能差异较大,破坏形式也不同,相同条件下,钢纤维混凝土的耐久性能显著降低。     

Reliability-based optimum design of reinforced concrete girders

A practical optimization approach to the design of reinforced concrete girders for highway bridges is presented. The approach is entirely based on the American Association of State Highway and Transportation Officials (AASHTO) standard specifications for highway bridges. All behavior and side constraints specified in the AASHTO bridge code are considered in the optimum design process. Two optimization formulations are presented. The first uses load and resistance design factors (LRFD) and the second one is entirely based on a reliability approach. In these formulations, the independent and dependent variables are identified, and the constraints are formulated in both the AASHTO-LRFD format and the AASHTO-reliability-based format. The solutions for both formulations are obtained by using a nonlinear optimization software. Numerical examples illustrate the application of the proposed approach to the design of reinforced concrete T-girders. Sensitivity analyses are also performed for finding the effects of various parameters including steel to concrete cost ratio and allowable reliability level on the optimum solution.     

Life-cycle cost analysis of reinforced concrete structures in marine environments

Chloride-induced corrosion of carbon steel reinforcement is the main cause of deterioration of reinforced concrete (RC) structures in marine environments. One of the ways to protect RC structures from corrosion is to use corrosion-resistant stainless steel reinforcing bars. However, stainless steel is between six and nine times more expensive than carbon steel. Thus, its use can only be justified on a life-cycle cost basis. In the paper a time-variant probabilistic model was presented to predict expected costs of repair and replacement which was then used to calculate life-cycle costs for RC structures in marine environments under different exposure conditions. Results of the life-cycle cost analysis can be applied to select optimal strategies improving durability of RC structures in marine environments, including the use of stainless steel reinforcement.     

基于ADINA对钢筋混凝土构件的推倒分析研究

介绍了ADINA中模拟钢筋混凝土的弯矩曲率梁单元,并应用该弯矩曲率梁单元对某桥墩进行了推倒分析,通过比较计算结果和试验曲线,认为ADINA弯矩曲率梁单元能合理模拟和分析钢筋混凝土结构,用弯矩曲率梁单元做推倒分析,计算过程简单、结果可靠度高。     

钢筋砼结构受硫酸盐腐蚀及其处理方法的几点探讨

为研究硫酸盐腐蚀下结构耐久性及其修复,本文主要针对钢筋混凝土结构,分析硫酸盐腐蚀的机理,论述了受蚀前提高钢筋混凝土结构耐久性的措施,探讨了修复和加固受蚀后钢筋混凝土结构的方法,并以一化工厂为例,在其受蚀后,采用添加一定比例外加剂的普通硅酸盐水泥进行修复,结果表明新老混凝土结合良好,工作状态正常。通过分析其腐蚀机理得到的修补措施行之有效。     

Structural reliability of concrete bridges including improved chloride-induced corrosion models

A structural deterioration reliability (probabilistic) model has been used herein to calculate probabilities of structural failure. New reinforced concrete corrosion initiation, corrosion rate and time-variant load models are proposed. Three durability design specifications are considered in a lifetime reliability analysis of a RC slab bridge. Time-variant increases in loads are considered also. It was found that the application of de-icing salts causes significant long-term deterioration and reduction in structural safety for poor durability design specifications. A reduced cover or increased water-cement ratio increases failure probabilities. When compared to the case of “no deterioration”, it was observed also that the probability of failure only marginally increased for good durability design specifications. The approaches described herein are relevant to other physical infrastructure also.     

A comprehensive probabilistic model of chloride ingress in unsaturated concrete

Corrosion induced by chloride ions has become a critical issue for many reinforced concrete structures. The chloride ingress into concrete has been usually simplified as a diffusion problem where the chloride concentration throughout concrete is estimated analytically. However, this simplified approach has several limitations. For instance, it does not consider chloride ingress by convection which is essential to model chloride penetration in unsaturated conditions as spray and tidal areas. This paper presents a comprehensive model of chloride penetration where the governing equations are solved by coupling finite element and finite difference methods. The uncertainties related to the problem are also considered by using random variables to represent the model’s parameters and the materials’ properties, and stochastic processes to model environmental actions. Furthermore, this approach accounts for: (1) chloride binding capacity; (2) time-variant nature of temperature, humidity and surface chloride concentration; (3) concrete aging; and (4) chloride flow in unsaturated conditions. The proposed approach is illustrated by a numerical example where the factors controlling chloride ingress and the effect of weather conditions were studied. The results stress the importance of including the influence of the random nature of environmental actions, chloride binding, convection and two-dimensional chloride ingress for a comprehensive lifetime assessment.     

高性能混凝土产业化发展的若干思考

本文通过对高强高性能混凝土的研究应用回顾,提出了普通混凝土高性能化是今后我国高性能混凝土产业化发展的主导方向,也是解决当前泵送混凝土普遍存在的早期开裂趋势明显的主要技术途径。对制约高性能混凝土产业化发展的水泥品质、现行规范和施工养护工艺等因素作了深入阐述。     

减缩剂对减少混凝土塑性收缩裂缝的影响

暴露在高蒸发速率环境下的新拌混凝土很容易产生塑性收缩裂缝,特别是表面积与体积的比率很大的时候,目前的研究都证明了,减少拌合水的表面张力是减少塑性裂缝的一种很有效的办法。我们将传统混凝土和高强混凝土掺加超塑化剂和减缩剂,在塑性阶段暴露干燥,测量毛细孔压、沉降、内部温度和蒸发速率,结果显示减缩剂对减少混凝土甚至是高强混凝土的塑性裂缝都是很有效的,这主要由于蒸发速率减少,原因是孔中弯液面的发展导致毛细管压的峰值出现延迟和较低的沉降率。     

砖混结构中钢筋混凝土构造柱、圈梁对抗震的作用

本文对砖混结构构造柱和圈梁从规范规定出发,通过构造柱和圈梁在砖混结构中的不同作用,结合“5．12”汶川大地震对构造柱和圈梁不规范的设计或施工造成砖混结构房屋的不同损坏情况,进行粗略分析构造柱和圈梁对砖混结构抗震所起到的主要关键作用,供今后的砖混结构的设计、施工有所参考。     

Finite element reliability analysis of bridge girders considering moment–shear interaction

Reliability analysis is necessary in bridge design to determine which parameters have the most significant influence on the structural response to applied loadings. To support finite element reliability applications, analytical response sensitivities are derived with respect to uncertain material properties, girder dimensions, reinforcing details, and moving loads by the direct differentiation method (DDM). The resulting expressions have been implemented in the general finite element framework OpenSees which is well suited to the moving load analysis of bridges. Numerical examples verify the DDM response sensitivity equations are correct, then a first-order reliability analysis shows the effect uncertain parameters have on the interaction of negative moment and shear force near the supports of a continuous reinforced concrete bridge girder. A unique contribution is the treatment of moment–shear interaction using Lamé curves with foci calculated from MCFT equations. In addition, the analysis demonstrates non-seismic bridge engineering applications that have been developed in the OpenSees framework.     

Sensitivity of uncertainties in performance prediction of deteriorating concrete structures

Deterioration models for the condition and reliability prediction of civil infrastructure facilities involve numerous assumptions and simplifications. Furthermore, input parameters of these models are fraught with uncertainties. A Bayesian methodology has been developed by the authors, which uses information obtained through health monitoring to improve the quality of prediction. The sensitivity of prior and posterior predicted performance to different input parameters of the deterioration models, and the effect of instrument and measurement uncertainty, is investigated in this paper. The results quantify the influence of these uncertainties and highlight the efficacy of the updating methodology based on integrating monitoring data. It has been found that the probabilistic posterior performance predictions are significantly less sensitive to most of the input uncertainties. Furthermore, updating the performance distribution based on ‘event’ outcomes is likely to be more beneficial than monitoring and updating of the input parameters on an individual basis.     

Spatial time-dependent reliability analysis of corroding pretensioned prestressed concrete bridge girders

Accelerated pitting corrosion tests have been performed to obtain spatial and temporal maximum pit-depth data for prestressing wires. This data is then used to develop probabilistic models of pitting corrosion and strength capacity of 7-wire strands. The probabilistic model of pitting corrosion for strands is then combined with a non-linear Finite Element Analysis and probabilistic models of corrosion initiation and propagation to study the spatial and temporal effects of pitting corrosion on a typical pretensioned prestressed concrete bridge girder. The limit states considered are flexural strength and serviceability. The spatial time-dependent reliability analysis takes into account the uncertainties and variabilities related to material properties, dimensions, loads and corrosion parameters as well as the spatial variability of pitting corrosion of prestressing strands. Including the spatial variability of pitting corrosion in the reliability analysis increased both the probability of strength and serviceability failure when compared with a mid-span sectional analysis.     

滨海环境下钢筋混凝土桥梁结构耐久性优化设计

滨海环境下钢筋混凝土桥梁结构的耐久性是受到广泛关注的问题,本文以江苏省临海高等级公路连云港段某大型桥梁工程为例,从原材料控制指标、配合比、设计强度等级与保护层厚度以及耐久性附加措施等几个方面,对滨海环境下桥梁混凝土结构方案进行了优化设计。     

Proportioning of reinforced concrete column sections

Relatively simplistic recommendations are widely available for the preliminary sizing of reinforced concrete columns. A simple, more precise approach is developed herein. The neutral axis depth and reinforcement required to provide a desired resistance to axial load and moment was determined analytically for the common case of symmetrically distributed reinforcement. Readily available solver routines are used to determine section dimensions required to provide the desired axial and flexural strength, for a desired reinforcement ratio. The approach is illustrated for two examples, including a case in which independent load combinations cause bending about each principal axis of the section.     

上海地区地下工程专用混凝土的应用研究

耐久性混凝土的胶凝材料用量少,抗裂性高减少了后期修补费用,既满足耐久性要求,又兼顾绿色化。随着上海轨道交通和隧道工程的迅速发展,地下工程混凝土对耐久性的要求越来越高。本文简述了聚羧酸类外加剂配制的耐久性混凝土在上海地区地下工程的应用情况、存在的问题及解决方法。     

人工砂对混凝土长期耐久性能的影响

本文结合相关混凝土耐久性试验方法,选取福州地区有代表性的人工砂,系统地研究了人工砂颗粒形貌及石粉含量对混凝土早期抗裂、收缩性、渗水高度等耐久性能的影响。     

冻融循环对钢筋与混凝土粘结性能的试验研究

在冻融循环作用下对钢筋混凝土试件进行粘结性能的试验研究,分析了随冻融循环次数的增加,极限粘结强度、平均滑移的变化趋势以及粘结—滑移关系曲线的变化,其结果可对混凝土结构耐久性设计提供依据,具有十分重要的理论意义和应用价值。     

氯离子侵蚀环境下混凝土结构耐久性寿命评估方法研究

根据氯离子侵蚀环境下混凝土结构中钢筋锈蚀的发生和发展,分析了结构性能的衰退过程,得到了氯离子侵蚀环境下结构耐久性寿命评估模型.考虑到寿命评估模型中主要参数的不确定性影响,基于Monte Carlo原理,采用CrvstalBall软件对混凝土构件进行了随机模拟.随机模拟结果显示,保护层厚度及氯离子浓度是影响氯离子侵蚀环境下混凝土结构耐久性寿命的重要参数.     

AC类稳定型橡胶改性沥青混凝土路用性能的研究

针对AC类稳定型橡胶改性沥青混凝土的高温性能、低温性能和抗水损害性能,采用车辙试验、低温弯曲试验和冻融劈裂试验方法,进行试验检测,通过数据的统计分析,提出了高温性能、低温性能和水稳定性的技术指标要求,为AC类稳定型橡胶改性沥青混合料配比设计和施工质量控制,提供依据和参考。